1. Field of the Invention
The present invention concerns generally a sound transducer for either receiving or transmitting sound, including subsonic, audible, and ultrasonic sound. In particular, the present invention is directed to a pressure-compensated sound transducer incorporating at least one piezoelectric element fixed to a concomitant flexural metal plate for use in ambient environments wherein the pressure is greater than that normally expected at the earth""s surface, especially in high-pressure hydrostatic or geostatic operating environments. For example, utilized either as a single element or combined in various two and three dimensional arrays, the present invention provides ambient pressure-compensation means for sound transducer systems used in either maritime or borehole environments by the petroleum industry for petroleum resource exploration, exploitation and monitoring.
2. Description of Related Art
The myriad benefits accrued from the sound transducer process of converting between mechanical and electrical energy has provided the impetus for many inventions, including the incorporation of dual piezoelectric elements in a single transducer assembly to gain certain signal conditioning advantages.
For example, FIG. 1, exploded perspective view, exemplifies a prior art uncompensated dual element piezoelectric transducer assembly. Uncompensated transducer assembly 1 comprises a ring support 3 that maintains a first flexural metal disk 7 and a second flexural disk 11 in a fixed relation to each other. First flexural disk 7 provides propagation medium coupling to first piezoelectric element 9 affixed thereto. In like manner, second piezoelectric element 13 is fixed to second flexural disk 11, the disk providing mechanical coupling between the medium and the piezoelectric element. Electrically connected in either series or parallel configurations, the dual piezoelectric assembly provides numerous signal-conditioning advantages.
Typically, transducer assembly 1 has been hermetically sealed to keep out foreign fluids and substances, and ring support void 5 is filled with a gas. Unfortunately, this manufacturing process created problems whenever the transducer was operated in ambient pressure environments considerably above normal atmospheric pressure. Numerous schemes have been employed to compensate for this problem. Some remedies entail the use of absorbent substances in the void of the transducer ring support. For example, filling the interior of the ring support housing with an absorbent material saturated with a fluid has been used in conjunction with opening the ring interior to the surrounding medium. U.S. Pat. No. 4,996,675 xe2x80x9cSIGNAL SENSOR INSENSITIVE TO STATIC PRESSURE VARIATIONSxe2x80x9d is incorporated herein by reference for purposes of indicating the background of the present invention or illustrating the mature state of the art for use of an absorbent material to compensate for the effects of ambient static pressure on the sensor.
The continuing quest for new petroleum resources has led exploration teams from relatively benign sites to sites where the environment is more extreme, and perhaps hazardous. This geographic shift has heightened the desire for simple, reliable, economical sound transducers, employing a minimum of parts and no moving parts, which can be operated in high ambient pressure environments.
It is an object of the present invention to provide a pressure compensated sound transducer incorporating at least one piezoelectric element and concomitant flexural metal plate, wherein the pressure compensation means is at least one mensurational duct, the duct having pre-determined duct mensural parameters derived from calculations, for communicating pressure compensating fluid between an inner reservoir and an outer reservoir, each piezoelectric element, each reservoir and the mensurational duct enclosed within a sealed, protective, compliant boot. It is an additional object of the present invention to provide a pressure compensated sound transducer incorporating at least one piezoelectric element and concomitant flexural metal disk, and at least one mensurational duct, wherein the transducer may be employed as either a sound receiving device, for example, a hydrophone, or a sound transmitting device, for example, a sound projector, and wherein the pressure compensation means is both passive and simple. It is a further objective of the present invention to provide a pressure compensated sound transducer incorporating at least one piezoelectric element and concomitant flexural metal disk, and at least one mensurational duct, wherein the pressure compensated sound transducer may be employed singly or assembled into an array, the array being a line array, a planar array, a volumetric array, or any combination thereof.